This invention relates to an input device for sewing machines which performs program control of sewing patterns, and more particularly, to an input device by which sewing patterns being prepared can be modified.
A sewing machine has heretofore been known which performs a sewing in a desired pattern by moving a work holder for supporting a workpiece by a pulse motor in accordance with coordinate date which has previously been stored as data corresponding to the desired sewing pattern in a memory device such as magnetic tape, magnetic card, and floppy. As an input device for this type of sewing machine there has been known an input device which inputs inflection points of sewing pattern to a digitizer (graph drawing apparatus) by means of indicating pen to prepare sewing patterns. The term "inflection point" as used herein means a point representing the contour of graphs. A straight line is represented by two inflection points, i.e. one end and the other end thereof. A circular arc is represented by three inflection points, i.e. one end, the other end, and a point on the arc therebetween. When points are inputted, the points themselves are inflection points. In the prior art input device of this type, the modification of a sewing pattern being prepared requires removal of every point to be eliminated or requires a new start for the newly desired pattern. This disadvantageously requires a considerable long period of time for the preparation of a desired pattern, complicates the operation, and makes it impossible to prepare a pattern conforming to the sewing machine.